Small style changes to --list-themes

assets/theme_preview.rs

@@ -1,5 +1,5 @@
-// Output the square of a number.
-fn print_square(num: f64) {
-    let result = f64::powf(num, 2.0);
-    println!("The square of {:.2} is {:.2}.", num, result);
-}
+  // Output the square of a number.
+  fn print_square(num: f64) {
+      let result = f64::powf(num, 2.0);
+      println!("The square of {:.2} is {:.2}.", num, result);
+  }